A certificate of analysis (COA) is the document that connects a vial on your bench to actual laboratory data. For research peptides it is the single most important quality record, yet many COAs are skimmed rather than read. This guide walks through each section of a typical peptide COA and what it does, and does not, prove.
What a COA is
A COA is a batch-specific report issued by the testing laboratory. It states which tests were run on a sample from a specific production lot, the methods used, the acceptance criteria and the results. A COA applies only to the batch it names, which is why the batch or lot number is the first thing to check.
The sections of a peptide COA
1. Product and batch identification
Look for the compound name, the batch or lot number, the date of analysis and the name of the laboratory. The batch number on the COA should match the label on the vial. A COA without a batch number, or with a date far older than the product, cannot be tied to the material you received.
2. Identity: mass spectrometry (MS)
Mass spectrometry measures the mass of the molecules in the sample. For a peptide, the observed mass should match the theoretical molecular weight calculated from its amino-acid sequence, usually within a small tolerance. This test answers the question “is this the right molecule?” It does not tell you how pure the sample is.
3. Purity: high-performance liquid chromatography (HPLC)
HPLC separates the components of a sample and records them as peaks on a chromatogram. Purity is reported as the area of the main peak as a percentage of the total peak area. A result such as 99.1% means that, under the conditions of that method, 99.1% of the detected signal came from the target peptide. Ask to see the chromatogram itself, not only the number.
4. Appearance and form
Most research peptides are supplied as a lyophilized (freeze-dried) white to off-white powder. The COA usually records the visual appearance of the tested sample.
5. Content or quantity (when reported)
Some COAs also report net peptide content or the measured amount per vial. HPLC purity and net content are different measurements: a sample can be highly pure yet contain counter-ions and residual water that contribute to the total weight.
What a COA does not tell you
- It does not cover other batches. Each lot needs its own COA.
- HPLC purity does not identify every impurity; it reports what the method detects.
- Unless stated, a standard COA does not include sterility, endotoxin or heavy-metal testing.
Red flags to check
- No batch number, or a batch number that does not match the vial.
- No laboratory name, or results that cannot be verified with the lab.
- Purity reported without a method or chromatogram.
- Identical COAs reused across different products or sizes.
- Observed mass that does not match the compound’s theoretical molecular weight.
How OxygenLab handles COAs
OxygenLab products are tested by independent third-party laboratories for identity and purity, and published certificates are on our COA page. If you need a specific batch report, contact us with the lot number.
Frequently asked questions
What is a good HPLC purity for a research peptide?
Many research suppliers specify a minimum of 98% or 99% HPLC purity. The right threshold depends on your experimental protocol.
Is mass spectrometry or HPLC more important?
Both. Mass spectrometry confirms identity; HPLC estimates purity. A reliable COA reports both.
Why should the COA batch number match my vial?
Test results apply only to the batch tested. Matching numbers is the only way to link the data to your material.
Research use only. OxygenLab products are supplied for in-vitro laboratory research and analytical use only. They are not for human or animal use and are not intended to diagnose, treat, cure or prevent any disease. See our Legal & Compliance policy.
Lab tool: Working out solution concentration? Try the free OxygenLab Peptide Calculator — enter vial mass and diluent volume to get mg/mL, µg/mL and molarity.
